In order to drive a synchronous machine such as a synchronous motor, information concerning the rotation speed and the rotation position of a rotor are indispensable. If a position detector such as an encoder is used, it is possible to know the rotation position of the rotor, and it is also possible to obtain the rotation speed from a change rate of the rotor position. However, there are defects in that the position detector is expensive, and complicated wiring is required in a case where an encoder is used. There have been invented many methods for driving a synchronous motor without using a position detector. In these methods, a voltage applied to the synchronous motor is controlled on the basis of a current of the synchronous motor, and driving of the synchronous motor is basically started from a stopped state.
Incidentally, in the case where the synchronous motor is driven from the idle state without using the position detector, the initial values of the rotation speed and the rotation position at the time of starting are indispensable. If a voltage detector is provided, the rotation speed and the rotation position can be easily known from an induced voltage in the idle state, however, in this case, since the voltage detector becomes redundantly necessary, the cost of the whole apparatus is raised.
Then, in order to start the driving of the synchronous motor from the idle state without using the position detector or the voltage detector, there has been devised a technique for detecting the rotation speed and the rotation position by short-circuiting all phases of terminals of the synchronous motor.
FIG. 18 is a block structural view showing a conventional rotation speed and rotation position detecting apparatus of a synchronous motor disclosed in, for example, Japanese Patent Laid-Open No. 11-75394.
In the drawing, reference numeral 1 designates an embedded magnet type synchronous motor including three-phase windings; 2, calculation means for outputting a voltage vector command and a trigger signal and for outputting a rotation speed and a rotation position in an idle state; 3, circuit means for applying voltages to respective phases of the synchronous motor 1 on the basis of the voltage vector command; and 4, detection means for detecting a current of the synchronous motor 1 on the basis of the trigger signal and for outputting the current to the calculation means 2.
Next, a detecting method of the rotation speed and the rotation position of a rotator in an idle state will be described. In the following, it is assumed that the rotation speed ω [rad/s] (electrical angular speed) in the idle state has a constant value, and the initial value of current is 0, and the winding resistance is neglected. Strictly, when the rotator is in the idle state and the terminals of the synchronous motor 1 are short-circuited in all phases, a torque is generated, so that the rotation speed ω is changed. However, in the case where the short circuit period is short, since the change of the rotation speed ω can be neglected, ω may be treated as a constant value. Besides, in the case where the short circuit period is short, since the attenuation of waveform by the winding resistance is also small, its value can also be neglected. Further, if a suitable voltage vector command is given to the circuit means 3, the initial value of current at the time of start of short-circuiting becomes 0. Incidentally, the voltage vector command given to the circuit means 3 will be described later.
The following expression is established on a rotating coordinate axis (d-q axis) rotating in synchronization with a rotator magnetic flux after t seconds from the start of short-circuiting.                               (                                                                      i                  d                                                                                                      i                  q                                                              )                =                  (                                                                                          ϕ                                          L                      d                                                        ⁢                                                                           ⁢                                      (                                                                  cos                        ⁢                                                                                                   ⁢                        ω                        ⁢                                                                                                   ⁢                        t                                            -                      1                                        )                                                                                                                                            -                                          ϕ                                              L                        q                                                                              ⁢                                                                           ⁢                  sin                  ⁢                                                                           ⁢                  ω                  ⁢                                                                           ⁢                  t                                                              )                                    (        1        )            where, id: d-axis component of current                iq; q-axis component of current        id: d-axis component of winding inductance        iq: q-axis component of winding inductance        ø: rotator magnetic flux        
On the other hand, the following expression is established between a current on a rest coordinate axis (a-b axis) and a current on the rotating coordinate axis (d-q axis).id2+iq2=ia2+ib2  (2) where, ia: a-axis component of current                ib: b-axis component of current        
Accordingly, when the currents ia and ib detected after T0 seconds from the start of short-circuiting are defined as ia01 and ib01, the following expression is established with respect to a current amplitude value Ia.                                                                         I                s                            =                            ⁢                                                                    i                    a01                    2                                    +                                      i                    b01                    2                                                                                                                          =                            ⁢                                                                                          ϕ                      2                                                              L                      d                      2                                                        ⁢                                                                           ⁢                                                            (                                                                        cos                          ⁢                                                                                                           ⁢                          ω                          ⁢                                                                                                           ⁢                                                      T                            0                                                                          -                        1                                            )                                        2                                                  +                                                                            ϕ                      2                                                              L                      d                      2                                                        ⁢                                                                           ⁢                                      sin                    2                                    ⁢                                                                           ⁢                  ω                  ⁢                                                                           ⁢                                      T                    0                                                                                                          (        3        )            where, T0: predetermined value satisfying 0<|ω|×T0<π/2.
The relation between the current amplitude value Ia and the absolute value |ω| of the rotation speed can be derived from the expression (3), and the relation is shown in FIG. 19. If the relation of FIG. 19 is stored in advance, the absolute value |ω| of the rotation speed can be uniquely obtained from the current amplitude value Ia. However, although the absolute value of the rotation speed can be derived from the expression (3), its rotation direction is unknown. Then, during a period shorter than a period of time in which the rotator makes a forward movement of 180 degrees in electrical angle when the rotator rotates at a maximum speed (regulated value), the voltage vector for short-circuiting the three-phase windings is changed to a voltage vector for making the current amplitude zero, and the value of the current is returned to 0. Successively, second all-phase short-circuiting is carried out, and a current after T0 from the start of the second short-circuiting is detected. The currents ia and ib detected at this time are defined as ia02 and ib02. From the magnitude relation between a current phase θc01 after T0 from the start of the first short-circuiting and a current phase θc02 after T0 from the start of the second short-circuiting, a sign of the rotation speed is judged.
The current phase θc01 can be obtained by calculating expression (4).                               θ          c01                =                              tan                          -              1                                ⁢                                           ⁢                                    i              b01                                      i              a01                                                          (        4        )            
Similarly, the current phase θc02 can be obtained by calculating expression (5).                               θ          c02                =                              tan                          -              1                                ⁢                                           ⁢                                    i              b02                                      i              a02                                                          (        5        )            
The sign of ω is judged from the sign of a difference between θc01 and θc02. The rotation speed ω can be detected from the above.
On the other hand, when currents on the d-g axis after T0 from the start of the second short-circuiting are defined as id02 and iq02 the relation of expression (6) is established with respect to the rotation position θ.                     θ        =                              θ            c02                    -                                    tan                              -                1                                      ⁢                                                   ⁢                                          i                q02                                            i                d02                                                                        (        6        )            The values of id02 and iq02 can be calculated by substituting the detected rotation speed ω and the short circuit time T0 for the expression (1). That is, from the detected rotation speed ω, the short circuit time T0, and the expression (6), the rotation position θ can be calculated.
From the above principle, in the above conventional apparatus, the voltage vector for short-circuiting the three-phase windings is twice outputted from the calculation means 2, the current of the synchronous motor 1 is once detected each time when the short-circuiting is carried out, and the rotation speed and the rotation posit ion of the synchronous motor in the idle state can be detected by using the plurality of detected current detection values.
The conventional apparatus will be described in more detail. FIG. 20 is a structural view of the circuit means 3 in the conventional apparatus shown in FIG. 18, and in the drawing, reference numeral 5 designates a semiconductor switch (for example, IGBT: Insulated Gate Bipolar Transistor) which is turned on and off based on a gate signal Q1; 6, a semiconductor switch turned on and off based on a gate signal Q2; 7, a semiconductor switch turned on and off based on a gate signal Q3; 8, a semiconductor switch turned on and off based on a gate signal Q4; 9, a semiconductor switch turned on and off based on a gate signal Q5; 10, a semiconductor switch turned on and off based on a gate signal Q6; and 11; a DC voltage source of a potential difference Ed.
Next, the operation of the circuit means 3 will be described. The circuit means 3 has the following eight switching modes.
Combination of gate signals Q1Switching modeto Q6 for turning on┌V0┘all are turned off┌V1┘Q1, Q5, Q6┌V2┘Q1, Q2, Q6┌V3┘Q4, Q2, Q6┌V4┘Q4, Q2, Q3┌V5┘Q4, Q5, Q3┌V6┘Q1, Q5, Q3┌V7┘Q1, Q2, Q3┌V8┘Q4, Q5, Q6The switching modes V7 and V8 are voltage vectors having a magnitude of 0, and the terminals of the synchronous motor 1 at this time are all-phase short-circuited. That is, the switching modes V7 and V8 are voltage vectors for short-circuiting the three-phase windings. The switching modes V1 to V6 are vectors having a phase difference of 60 degrees between adjacent ones and the magnitudes of V1 to V6 are equal to one another. In the switching mode V0, the current flowing through each phase of the synchronous motor 1 flows through the inside of the circuit means 3 in the direction to charge the DC voltage source 11, and the value of the current of the synchronous motor 1 is returned to 0 at the time when the current flowing through each phase is attenuated to 0. That is, when the switching mode is made V0, it is possible to return the value of the current of the synchronous motor 1 to 0 irrespective of a rest state or an idle state.
FIG. 21 is a structural view of the detection means 4, and in the drawing, reference numeral 12 designates a current detector for detecting a U-phase current; 13, a current detector for detecting a V-phase current; 14, a current detector for detecting a W-phase current; 15, a signal converter for sample-holding a signal obtained from the detector 12 at the rising time of a trigger signal, converting an analog signal into a digital signal, and outputting a U-phase current detection value; 16, a signal converter for sample-holding a signal obtained from the detector 13 at the rising time of a trigger signal, converting an analog signal into a digital signal, and outputting a V-phase current detection value; and 17, a signal converter for sample-holding a signal obtained from the detector 14 at the rising time of a trigger signal, converting an analog signal into a digital signal, and outputting a W-phase current detection value.
From the above structure, the detector 4 samples the current of each phase at the rising time of the trigger signal and converts it into the digital signal to output it.
FIG. 22 is a structural view of the calculation means 2, and in the drawing, reference numeral 18 designates an input circuit for inputting a detection current; 19, a CPU; 20, a memory for storing a program; 21, an output circuit for outputting a voltage vector command; 22, an output circuit for outputting a trigger signal; and 23, an output circuit for outputting a rotation position 8 and a rotation speed ω.
FIG. 23 is a view showing an example of relations between the time and the switching mode in the voltage vector command outputted by the calculation means 2 to the circuit means 3, the current amplitude value Is calculated in the calculation means 2, and the trigger signal outputted by the calculation means 2 to the detection means 4. In FIG. 23, at time t0, the calculation means 2 changes the switching mode which has been outputted from the output circuit 21 to the circuit means 3, from V0 to V7. Then, at a point of time (time t0) when a predetermined period T0 has elapsed, the calculation means changes the switching mode outputted to the circuit means 3 from V7 to V0, and at the same time, outputs the trigger signal from the output circuit 22.
The detection means 4 outputs the respective currents of U, V and W phases at the time when the trigger signal rises, that is, at the time, t1 to the calculation means 2. Then, after the currents iu, iv and iw are inputted from the input circuit 18, a program stored in the memory 20 in advance is executed by the CPU 19.
The following expression (7) is established between the respective currents iu, iv, iw of the U, V, W phases and ia, ib.                               (                                                                      i                  a                                                                                                      i                  b                                                              )                =                                            2              3                                ⁢                                           ⁢                      (                                                            1                                                                      -                                          1                      2                                                                                                            -                                          1                      2                                                                                                                    0                                                                                            3                                        2                                                                                        -                                                                  3                                            2                                                                                            )                    ⁢                                           ⁢                      (                                                                                i                    u                                                                                                                    i                    v                                                                                                                    i                    w                                                                        )                                              (        7        )            
The calculation means 2 calculates ia01, ib01, and Ic01, and Ia in accordance with the expressions (3), (4) and (7). Then, on the basis of Ia and the relation of FIG. 19 stored in advance, the absolute value |ω| of the rotation speed is obtained, and θc01 and |ω| are stored.
After the circuit means 3 outputs the switching mode V0, in the inside of the circuit means 3, the current flowing through each phase flows in the direction to charge the DC voltage source 11, and the value of the current of the synchronous motor 1 returns to 0 (time t2). Thereafter, after a period shorter than a period of time in which the rotator makes a forward movement of 180 degrees in electrical angle when the rotator rotates at the maximum speed (rated value) has elapsed (time t3), the calculation means 2 changes the switching mode outputted to the circuit means 3 again from V0 to V7. Then, at a point of time (time t4) when a predetermined period T0 has elapsed, the calculation means 2 changes the switching mode outputted to the circuit means 3 from V7 to V0, and at the same time, outputs the trigger signal. The detection means 4 outputs the respective currents of U, V and W phases at the rising time of the trigger signal, that is, at the time t4 to the calculation means 2. The calculation means 2 calculates ia02, ib02 and θc02 in accordance with the expressions (5) and (7), and determines the sign of the rotation speed ω from the magnitude relation between θc01 and θc02, and simultaneously calculates the rotation position θ using the expressions (1) and (6). The calculation means 2 outputs ω and θ obtained by the above processing as the rotation speed and the rotation position from the output circuit 23.
The conventional rotation speed and rotation position detecting apparatus of the synchronous machine has problems as follows.
Since the sign of the rotation speed can not be detected through one occurrence of short-circuiting, it has been necessary to short-circuit twice in order to detect the sign of the rotation speed. Besides, since the sign of the rotation speed is indispensable for the detection of the rotation position, it has been necessary to short-circuit twice in order to detect the rotation position as well. That is, since it has been necessary to short-circuit twice to detect the rotation speed and the rotation position, it takes a time to detect the rotation speed and the rotation position, and there has been a problem in that it takes a time to start up.
Besides, since the period of the short circuit is set constant, the value of the detected current becomes low in the idle state in which the rotation speed is low. As a result, there has been a problem in that detection accuracy is deteriorated by the influence of detection noise, cancellation of significant digit of an AD converter, or the like. In order to solve the problem, there is devised a method in which in the case where the value of the detection current is low, a short circuit period is again set longer and detection is again made. However, in this case, since the number of times of detection is increased, it takes a time to detect the rotation speed and the rotation position, and there has been a problem in that it takes a time to start up.
Further, in the process for calculating the rotation position since the phase difference between the rotation position θ and the current phase θc02 is changed in accordance with the rotation speed, there has been problems in that calculation must be made each time when and it takes a time. Besides, since this calculation uses an arc tangent function, there has been a problem in that complicated calculation is required.
The present invention has been made to solve the above problems, and has an object to provide an apparatus and a method in which a rotation state of a synchronous machine can be detected in a short time, and further has an object to provide an apparatus which can detect a rotation state with accuracy and ease.